Fluoride detection with the naked eye

07 February 2006

An effective sensor for the visual detection of fluoride in water has been developed by chemists in China.

Chun-ying Duan, Zhi-ping Bai and colleagues at the State Key Laboratory of Coordination Chemistry in Nanjing have made a ruthenium compound that changes colour from orange to blue-violet when it bonds to a fluoride anion.

The system contains a photoactive ruthenium bipyridine segment that enhances bonding to the fluoride anion through electrostatic interactions. This provides the dramatic colour change that can be observed by a naked eye.

There is a growing market for simple and affordable fluoride detection systems. Fluoride has an established role in preventing tooth decay and is currently being explored as a treatment for osteoporosis. However, overexposure can also lead to fluorosis, a type of fluoride toxicity that can lead to pitting of tooth enamel and discolouration and is rare in the UK. Until now, there have been no compounds that provide a measurable output when they bind to fluoride anions.

The sensor can be prepared as a test-paper, similar to pH paper, and no spectroscopic instrumentation is required. It is highly selective and can detect fluoride in aqueous solutions at a lower limit of about 10 ppm.

"Until now, there have been no compounds that provide a measurable output when they bind to fluoride anions."

Duan and Bai hope that this cheap and effective new sensor will prove advantageous in helping to prevent fluorosis in undeveloped regions.